The conventional photoresist resin material extensively used in the present semiconductor production process, particularly the one used in an extremely fine pattern fabrication process is comprised of various combinations of amorphous high molecular resins. However, referring to FIG. 1, in a conventional photoresist resin layer 100, upon light irradiation, light flux 101 incident on the surface of said photoresist layer 100 is diffused isotropically, or vertically as well as horizontally, in said resist layer as illustrated in the drawing, and thus, the mask pattern is spread out and out of focus during said light propagation in said layer 100 even when a light pattern of high contrast and identical dimension is projected on said layer 100.
Therefore, in a case of a reduction projection aligner, a focus depth f is less than the thickness of said photoresist layer 100, and therefore, exactly reproduced images are formed only in a limited portion 100 A in said photoresist layer 100, and only blurred and out of focus images are produced in portions 100B and 100C.
Furthermore, if there exists a surface roughness 201 in an aluminum or other material layer 202 formed on said substrate 200 as shown in FIG. 2, said incident light is scattered by said roughness and is propagated in said photoresist layer 100 in random directions and lower the image contrast, thus in a positive type photoresist, the line width will become narrower and in a negative type photoresist, the line width will be broadened producing large dimensional errors between the mask pattern and the pattern reproduced in the photoresist, and an exact reproduction of the original pattern is difficult to obtain.